The present invention relates to addressing in a communications network and in particular to addressing in a communications network in which network nodes are split into a call control part and a bearer control part.
Telecommunications networks currently rely to a large extent upon the Signalling System no.7 (SS7) as the mechanism for controlling call connections and for handling the transfer of signalling information between signalling points of the networks. Typically, one or more application and user parts at a given signalling point will make use of SS7 to communicate with peer application and user parts at some other signalling point. Examples of user parts are ISUP (ISDN User Part) and TUP (Telephony User Part) whilst examples of application parts are INAP (Intelligent Network Application Part) and MAP (Mobile Application Part). The conventional SS7 protocol stack includes Message Transfer Parts MTP1, MTP2, and MTP3 which handle the formatting of signalling messages for transport over the physical layer as well as various routing functions.
There has been considerable interest of late amongst the telecommunications community in using non-standard (i.e. non-conventional within the telecommunications industry) signalling transport mechanisms in telecommunications networks in place of the conventional SS7 mechanisms. The reasons for this are related both to improvements in efficiency as well as potential cost savings. Much consideration has been given for example to the use of Internet Protocol (IP) networks to transport signalling information between signalling points. IP networks have the advantage that they make efficient use of transmission resources by using packet switching and are relatively low in cost due to the widespread use of the technology (as opposed to specialised telecommunication technology). There is also interest in using other transport mechanisms including AAL1/2/5, FR etc.
ISUP, which deals with the setting-up and control of call connections in a telecommunications network, is closely linked to the SS7 signalling transport mechanism and does not readily lend itself to use with other non-standard transport technologies such as IP and AAL2. As such, several standardisation bodies including the ITU-T, ETSI, and ANSI, are currently considering the specification of a signalling protocol for the control of calls, which is independent of the underlying transport mechanism. This is illustrated in FIG. 1 and can be viewed as separating out from the protocol, Bearer Control functions which relate merely to establishing the parameters (including the start and end points) of the “pipe” via which user plane data is transported between nodes, and which are specific to the transport mechanism. The new protocol, referred to as Bearer Independent Call Control (BICC) or Transport Independent Call Control (TICC), retains Call Control functions such as the services invoked for a call between given calling and called parties (e.g. call forwarding), and the overall routing of user plane data.
The new network architecture resulting from the separation of the Call and Bearer Control levels results in an open interface appearing between a Call Control entity and a Bearer Control entity, where these entities are referred to as a Media Gateway Controller and a Media Gateway respectively. The open interface is referred to hereinafter as X-CP, examples of which are the MEGACO work of the IETF and the H.248 work of ITU Study Group 16 (SG16). It is envisaged that a given Media Gateway Controller may control several Media Gateways.
Despite the decoupling of the Call and Bearer Control levels, it remains necessary to convey information about the Bearer Control level at the Call Control level in order to establish bearer connections between Media Gateways for a call. In particular, it is necessary to convey on a per call basis the addresses of Media Gateways between peer Media Gateway Controllers, where the identified Media Gateways are responsible for handling the bearer connection for the call. Current proposals are to provide an addressing mechanism in the BICC protocol which is specific to ITU-T E.164 addresses.